A nuclear power plant operating with a closed working-gas cycle comprises a nuclear reactor serving as the main heating source for a working gas which can then be introduced into a power-generating turbine in which it expands and converts the energy of expansion into useful work in driving the turbine. The latter is connected to an electric-current generator whose output may operate a load, i.e., may be connected to electrical mains supplying the consumer.
Generally residual useful heat of the gas, after it has traversed the power-generating turbine, is recovered in a recuperative heat exchanger which can be used to preheat the gas before it is fed through the nuclear reactor for main heating.
After passing through the recuperative heat exchanger, the gas may be compressed in multiple stages with intervening cooling before being preheated as described in continuation of the closed cycle.
Various systems have been proposed to obtain maximum utilization of the nuclear energy produced by the reactor. For example, in nuclear-energy plants operating with closed working-gas cycles, especially in a nuclear-energy installation in which the working gas is heated in so-called high-temperature reactors, it is known to provide a plurality of closed working-gas cycles in parallel. In such so-called "multiloop" systems it is easier to utilize the total heated gas quantity. However, conventional multiloop systems involve various problems, costs and characteristics, as described below, which have limited the applicability of multiloop principles.
For example, German printed application (Offenlegungsschrift) DT-OS 22 41 426 discloses a nuclear power plant with closed working-gas cycle in which a plurality of parallel flow cross-sections are provided within the reinforced-concrete vessel surrounding the nuclear reactor core and serving to heat or to cool partial gas streams in parallel.
The working gas is then conducted to a turbine set in a separate chamber below the reactor from which the gases flow through separate but parallel heat exchangers to give up residual useful heat.
The disadvantage of this system is that, when it is necessary to repair the turbine set, the entire installation must be brought to a standstill. Also this arrangement provides a low-pressure compressor and a high-pressure compressor on the rotor shaft of the turbine set, whereby making the shaft undesirably long and massive. Finally, the location of the turbine set below the reactor core complicates the gase-feed and gas-discharge ducts at the turbine set. From this results a large necessary space within reinforced concrete so that the capital cost of the installation is relatively high.
A further system has been disclosed in German printed application (Offenlegungsschrift) DT-OS 17 64 249 in which the nuclear power plant has a plurality of gas-circulation loops, each of which is provided with all of the components necessary for the circulation of the gas. Compression of the working gas in each loop is carried out with separate compressors and with intervening cooling in separate coolers.
The advantage obtained by this subdivision of the heated gas flow into several partial streams is at the expense of the disadvantage that long gas paths are required. Furthermore, apart from the energy-producing turbine it is necessary to provide a turbine set comprising a turbine and three compressors for each of the partial gas streams and to provide between each of these compressors, a respective cooler. The capital cost of setting up three such identical loops is thus high and a corresponding gain in overall plant efficiency, as compared with, for example, a single loop system is not always obtained.